Method of enhancing clear field phase shift masks with border regions around phase 0 and phase 180 regions

ABSTRACT

A technique in which a first boundary region is added to the ends of phase zero ( 0 ) pattern defining polygons and a second boundary region is added to the ends of phase  180  pattern. This technique can improve line end pattern definition and improve the manufacturability and patterning process window. The added boundary region balances the light on both sides of the line ends, resulting in a more predictable final resist pattern.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.10/016,439, Attorney Docket No. 39153/447 (G1152), entitled METHOD OFEXTENDING THE AREAS OF CLEAR FIELD PHASE SHIFT GENERATION; U.S. patentapplication Ser. No. 10/016,710, Attorney Docket No. 39153/448 (G1153),entitled METHOD OF ENHANCING CLEAR FIELD PHASE SHIFT MASKS WITH CHROMEBORDER AROUND PHASE 180 REGIONS; U.S. patent application Ser. No.10/016,702, Attorney Docket No. 39153/449 (G1154), entitled METHOD OFENHANCING CLEAR FIELD PHASE SHIFT MASKS BY ADDING PARALLEL LINE TO PHASE0 REGION; and U.S. patent application Ser. No. 10/016,441, AttorneyDocket No. 39153/451 (G1156), entitled METHOD OF ENHANCING CLEAR FIELDPHASE SHIFT MASKS WITH BORDER AROUND OUTSIDE EDGES OF PHASE ZEROREGIONS, all of which are assigned to the same assignee as the presentapplication.

FIELD OF THE INVENTION

The present invention relates generally to integrated circuits andmethods of manufacturing integrated circuits. More particularly, thepresent invention relates to generating phase shifting patterns toimprove the patterning of gates and other layers, structures, or regionsneeding sub-nominal dimensions.

BACKGROUND OF THE INVENTION

Semiconductor devices or integrated circuits (ICs) can include millionsof devices, such as, transistors. Ultra-large scale integrated (ULSI)circuits can include complementary metal oxide semiconductor (CMOS)field effect transistors (FET). Despite the ability of conventionalsystems and processes to fabricate millions of IC devices on an IC,there is still a need to decrease the size of IC device features, and,thus, increase the number of devices on an IC.

One limitation to achieving smaller sizes of IC device features is thecapability of conventional lithography. Lithography is the process bywhich a pattern or image is transferred from one medium to another.Conventional IC lithography uses ultra-violet (UV) sensitivephotoresist. Ultra-violet light is projected to the photoresist througha reticle or mask to create device patterns on an IC. Conventional IClithographic processes are limited in their ability to print smallfeatures, such as contacts, trenches, polysilicon lines or gatestructures.

Generally, conventional lithographic processes (e.g., projectionlithography and EUV lithography) do not have sufficient resolution andaccuracy to consistently fabricate small features of minimum size.Resolution can be adversely impacted by a number of phenomena including:diffraction of light, lens aberrations, mechanical stability,contamination, optical properties of resist material, resist contrast,resist swelling, thermal flow of resist, etc. As such, the criticaldimensions of contacts, trenches, gates, and, thus, IC devices, arelimited in how small they can be.

For example, at integrated circuit design feature sizes of 0.5 micronsor less, the best resolution for optical lithography technique requiresa maximum obtainable numerical aperture (NA) of the lens systems.Superior focus cannot be obtained when good resolution is obtained andvice versa because the depth of field of the lens system is inverselyproportional to the NA and the surface of the integrated circuit cannotbe optically flat. Consequently, as the minimum realizable dimension isreduced in manufacturing processes for semiconductors, the limits ofconventional optical lithography technology are being reached. Inparticular, as the minimum dimension approaches 0.1 microns, traditionaloptical lithography techniques may not work effectively.

With the desire of reducing feature size, integrated circuit (IC)manufacturers established a technique called “phase shifting.” In phaseshifting, destructive interference caused by two adjacent translucentareas in an optical lithography mask is used to create an unexposed areaon the photoresist layer. Phase shifting exploits a phenomenon in whichlight passing through translucent regions on a mask exhibits a wavecharacteristic such that the phase of the light exiting from the maskmaterial is a function of the distance the light travels through themask material. This distance is equal to the thickness of the maskmaterial.

Phase shifting allows for an enhancement of the quality of the imageproduced by a mask. A desired unexposed area on the photoresist layercan be produced through the interference of light from adjacenttranslucent areas having the property that the phase of the lightpassing through adjacent apertures is shifted by 180 degrees relative toeach other. A dark, unexposed area will be formed on the photoresistlayer along the boundary of the phase shifted areas caused by thedestructive interference of the light which passes through them.

Phase shifting masks are well known and have been employed in variousconfigurations as set out by B. J. Lin in the article, “Phase-ShiftingMasks Gain an Edge,” Circuits and Devices, March 1993, pp. 28-35. Theconfiguration described above has been called alternating phase shiftmasking (PSM).

In some cases, phase shifting algorithms employed to design phaseshifting masks define a phase shifting area that extends just beyondactive regions of an active layer. The remaining length of polysilicon,for example, is typically defined by a field or trim mask. However, thisapproach is not without its problems. For example, alignment offsetsbetween phase shift masks and field masks may result in kinks or pinchedregions in the polysilicon lines as they transition from the phaseshifting area to the field mask areas. Also, since the field masks areemployed to print the dense, narrow lines of polysilicon beyond theactive regions, the field masks become as critical and exacting as thephase shift masks.

Phase shift patterning of polysilicon or “poly” layouts has been provento be an enhancement in both manufacturing as well as enabling smallerpatterned lines and narrow pitches. These items can be more enhanced asthe desired linewidth and pitch shrinks, yet there can be some risks andcomplications.

Conventional patterning with phase shifters has been done by shiftingonly the areas of minimum desired dimensions—usually the poly gate ornarrow poly that is over the active pattern. The patterned poly linesthat are away from the active regions are usually laid out with similardesign rules as that of the patterned poly lines on active regions. Assuch, there can be many transitions between the phase shifted patterningand binary patterning. Transition areas can result in linewidth loss,increasing device leakage.

Current alternating phase shift masking (PSM) designs for polysiliconlayers often focus on enabling gate shrink by applying alternating phaseshift regions around the gate region (i.e., the intersection of thepolysilicon and active layers). One such alternating PSM design isdescribed in U.S. Pat. No. 5,573,890 entitled METHOD OF OPTICALLITHOGRAPHY USING PHASE SHIFT MASKING, by Christopher A. Spence (one ofthe inventors of the present application) and assigned to the assigneeof the present application.

An enhanced phase shift approach was developed to reduce the transitionregions and move those regions away from the active edge to wider polyor corners of poly patterns where linewidth loss would have little or noimpact. Examples of this enhanced phase shifting approach are describedin U.S. patent application Ser. No. 09/772,577 entitled PHASE SHIFT MASKAND SYSTEM AND METHOD FOR MAKING THE SAME, filed on Jan. 30, 2001, byTodd P. Lukanc (one of the inventors of the present application) andassigned to the assignee of the present application, incorporated hereinby reference, now U.S. Pat. No. 6,534,224.

The specification of the Lukanc patent application describes binary andphase masks that define parts of the poly pattern and need to have verycontrolled critical dimensions (CDs). The phase mask basically has longnarrow openings that are easy to pattern but the binary mask has bothsmall openings as well as small lines, in both isolated and dense areas.As such, the patterning of the binary mask can be complicated and themanufacturing window of this technique can be limited. In both thesimple phase and the enhanced phase methods, both masks are critical andhave different optimized illumination and patterning conditions.

Other known systems use a “node” based approach rather than agate-specific approach to generate a phase assignment that attempts toapply phase shifting to all minimum poly geometries (both field andgate). Two examples of the “node” based approach include, for example,Galan et al. “Applications of Alternating-Type Phase Shift Mask toPolysilicon Level for Random Logic Circuits,” Jpn. J. Appl. Phys. Vol.33 (1994) pp. 6779-6784, December 1994, and U.S. Pat. No. 5,807,649entitled LITHOGRAPHIC PATTERNING METHOD AND MASK SET THEREFOR WITH LIGHTFIELD TRIM MASK, by Liebmann et al.

In view of the known art, there is a need for improvements to the clearfield phase shifting mask (PSM) and field or trim mask approach thatresult in simpler and more reliable mask fabrication and in better waferimaging. Further, there is a need to minimize variations or use ofoptical proximity correction (OPC) by enclosing phase shift maskingfeatures. Yet further, there is a need to generate phase shiftingpatterns to improve the patterning of gates and other layers needingsub-nominal dimensions.

SUMMARY OF THE INVENTION

The present invention is related to a technique in which a boundaryregion is added to the ends of phase zero (0) pattern defining polygonsas well as to outside edges of phase 180 regions. This technique canimprove line end pattern definition and improve the manufacturabilityand patterning process window. The added boundary region makes maskinspection easier, defines the phase etch region with chrome, balancescoma and other patterning issues, and balances the light on both sidesof the line ends, resulting in a more predictable final resist pattern.

An exemplary embodiment is related to a method of designing a phaseshift mask. This method can include identifying edges of a first phaseregion of a phase shifting mask, expanding the identified edges todefine a narrow line along the edges of the first phase region, andforming a phase region boundary in the narrow line along the edges ofthe first phase region. The first phase region is located proximate acritical poly region and the identified edges are not edges of the firstphase region adjacent to the critical poly region.

Another exemplary embodiment is related to a method of generating phaseshifting patterns to improve the patterning of gates and other layersneeding sub-nominal dimensions. This method can include definingcritical gate areas, creating phase areas on either side of the criticalgate areas, assigning opposite phase polarities to the phase areas oneither side of the critical gate areas, enhancing phase areas withassigned phase polarities, defining break regions where phasetransitions are likely to occur, generating polygons to define otheredges and excluding the defined break regions, and constructing aboundary region outside of phase 0 regions to form a phase shift border.

Another exemplary embodiment is related to a method of enhancing clearfield phase shift masks with a chrome border around outside edges ofphase 0 and phase 180 regions. The method can include assigning phasepolarities to phase areas where the phase areas include first phaseareas and second phase areas, defining edges of the assigned phaseareas, establishing a first boundary around the defined edges of thefirst phase area, forming a chrome border in the first boundary aroundthe first phase area, establishing a second boundary around the addededges of the second phase area, and forming a phase shift border in thesecond boundary around the second phase area.

Another exemplary embodiment relates to a mask configured for use in anintegrated circuit manufacturing process. This mask can include acritical poly section defined by first edges of a phase zero region andfirst edges of a phase 180 region, a first chrome boundary regionlocated outside second edges of the phase 180 region, and a secondchrome boundary region around second edges of the phase 0 region. Thesecond edges of the phase 180 region are different than the first edgesof the phase 180 region, wherein the chrome boundary region includes anopaque material. The second edges of the phase 0 region are differentthan the first edges of the phase 0 region.

Other principle features and advantages of the invention will becomeapparent to those skilled in the art upon review of the followingdrawings, the detailed description, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The exemplary embodiments will hereafter be described with reference tothe accompanying drawings, wherein like numerals denote like elements,and:

FIG. 1 is a flow diagram illustrating steps in a method of forming aphase shift mask according to an exemplary embodiment;

FIG. 2 is a top planar view of a phase shift mask design in accordancewith an exemplary embodiment;

FIG. 3 is a top planar view of a field or trim mask design configuredfor use with the phase shift mask design of FIG. 2 in accordance with anexemplary embodiment;

FIG. 4 is a block illustration of a portion of a poly line separating aphase 180 region and a phase 0 region and a corresponding trim mask inaccordance with an exemplary embodiment; and

FIG. 5 is a block illustration of a portion of a poly line separating aphase 180 region and a phase 0 region and a corresponding trim mask inaccordance with an exemplary embodiment.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 illustrates a flow diagram 100 depicting exemplary steps in theformation or design of a phase shifting mask (PSM) and a field or trimmask. A set of previously defined phase 0 or phase 180 regions on aphase mask help identify a critical poly section. These phase 0 or phase180 regions can be created by hand drawing, by using a currentlyavailable software program, or by creating an optimized program todefine the regions.

In a step 110, a chrome boundary region is formed on the phase maskoutside phase 180 region edges of the previously defined phase 180regions that are not defining a final poly pattern. This chrome boundaryregion can be defined by either hand drawing or by using a computersoftware program. Advantageously, this chrome boundary region makes iteasy to inspect the mask, and easy to pattern the phase etch step ofmaking the mask. In a step 120, all regions not defined (either as thefinal poly pattern or phase 180 regions or chrome boundary regions) aredefined as phase 0.

In a step 130, a chrome boundary region is added around the outside ofthe initially defined phase 0 regions proximate the critical polysections. Adding such a chrome boundary region helps to minimizepatterning issues.

In a step 140, the chrome is patterned and etched on the mask. As partof the chrome defining process or after the chrome is patterned, a layerof resist is coated and sections of the resist are selectively removedin areas where phase 180 sections are to be formed. In an exemplaryembodiment, an oversized phase 180 pattern, or a phase etch region, isdefined to allow the resist to be removed and the quartz to be etched.This oversized resist pattern covers any openings in the chrome where itis desired to avoid etching. A dry or wet etch can be used to etch thequartz to a lesser thickness in the formation of the phase 180 regions.The formation of phase 180 sections and phase etch regions are furtherdescribed with reference to FIG. 2.

In a step 150, the trim mask is formed to have openings that areoversized versions of the boundary chrome regions outside the final polypattern. The openings of the trim mask are oversized because their sizeis slightly larger in area than the boundary regions. In the trimmasking process, the openings of the trim mask are placed over theseslightly smaller boundary regions. An exemplary trim mask is describedwith reference to FIG. 3.

FIG. 2 illustrates a plan view of a phase mask 200 formed or designedutilizing the process described with reference to FIG. 1. Phase mask 200includes poly regions 210, phase 180 regions 220, phase 0 regions 230,and phase 180 boundary regions 240. Poly regions 210 (depicted in FIG. 2as cross-hatched areas) are critical poly sections. Phase 180 regions220 and phase 0 regions 230 help to define poly regions 210 and can becreated by hand or using a computer software program configured for thedesigning of phase masks. Phase 180 boundary regions 240 can be formedoutside edges of defined phase 180 regions 220 that are not defining thepoly pattern.

Phase mask 200 also can include a region 250 outside of defined areas.In an exemplary embodiment, region 250 (depicted in FIG. 2 withouthashing) is assigned a phase of zero.

Phase etch boxes 260 (depicted in FIG. 2 using a bold dashed line) areareas that define a pattern used in the formation of phase 180 regions220. Advantageously, the positions of phase etch boxes 260 areself-aligned to the chrome pattern as to avoid misplacement of the etchpattern relative to the original chrome pattern. In an alternativeembodiment, it is possible to make the etch profile such that itpartially goes underneath the chrome to partially hide the etch profile.The partially hidden etch profile allows for some variation in sidewallprofiles.

Trim mask openings 270 (depicted in FIG. 2 using a dotted line) definean area that is exposed when the field or trim mask is applied. Anexemplary trim mask corresponding to trim mask openings 270 is describedwith reference to FIG. 3.

Phase mask 200 can also include chrome boundary regions 290 around theoutsides of phase 0 regions 230. A trim mask corresponding to phase mask200 can include an oversize of all chrome regions outside the final polypattern.

FIG. 3 illustrates a plan view of a field or trim mask 300. Trim mask300 is configured for use with phase mask 200 described with referenceto FIG. 2. Trim mask 300 includes openings 310 corresponding to trimmask opening 270 in FIG. 2.

FIG. 4 illustrates a poly line mask 400 and a trim mask 405. Poly line400 separates a phase 180 region 410 and a phase 0 region 420. A chromeboundary 430 is located along edges of phase 180 region 410. Chromeboundary 430 can improve mask generation by allowing a chrome mask tofully define the quartz etch. Configured as such, however, poly linemask 400 is asymmetric and has a risk of bridging between adjacentlines.

FIG. 5 illustrates a poly line mask 500 and a trim mask 505. Poly linemask 500 separates a phase 180 region 510 and a phase 0 region 520. Achrome boundary 530 is located along edges of phase 180 region 510. Aphase region 540 is located along edges of phase 0 region 520. Byplacing phase region 540 or dummy lines at the edges of the phase 0region, symmetry is enhanced and, therefore, wafer patterning can beimproved.

Exemplary materials for chrome boundary 530 can include any material ofopaque qualities. Alternatively, other suitable opaque materials can beutilized for boundary 530, such as any material known to a person ofskill in the art to satisfy necessary phase requirements. Chromeboundary 530 can have a width of approximately a minimum gate widthdimension or the width between phase 0 and phase 180 regions where thecritical gates are formed.

Advantageously, the process described with reference to the FIGURESimproves gate width control, line end pattern definitions, and thepatterning process window. Moreover, the process can make the criticalpiece of the trim mask similar to that of the phase mask, namely arelatively narrow opening in the chrome mask (or a trench). Making thecritical piece of trim mask similar to the phase mask has an advantageof making the optimized illumination conditions of the phase mask moresimilar to or the same as the trim mask. By doing this, the stepper doesnot have to change settings (e.g., numerical aperture or partialcoherence or focus or exposure dose).

While the exemplary embodiments illustrated in the FIGURES and describedabove are presently preferred, it should be understood that theseembodiments are offered by way of example only. Other embodiments mayinclude, for example, different techniques for creating phase shiftingregions. Furthermore, other embodiments may use phase angles other than0 and 180 while still having a difference of 180. The invention is notlimited to a particular embodiment, but extends to variousmodifications, combinations, and permutations that nevertheless fallwithin the scope and spirit of the appended claims.

What is claimed is:
 1. A method of designing a phase shift mask, themethod comprising: identifying edges of a first phase region of a phaseshifting mask, the first phase region being located proximate a criticalpoly region and the identified edges not being edges of the first phaseregion adjacent to the critical poly region; expanding the identifiededges to define a narrow line along the edges of the first phase region;and forming a phase region boundary in the narrow line along the edgesof the first phase region.
 2. The method of claim 1, further comprising:identifying edges of a phase 180 region of a phase shifting mask, thephase 180 region being located proximate a critical poly region and theidentified edges not being edges of the phase 180 region adjacent to thecritical poly region; expanding the identified edges to define a narrowline along the edges of the phase 180 region; and forming chrome in thenarrow line to form a chrome boundary along the edges of the phase 180region.
 3. The method of claim 1, further comprising: assigning phasepolarities to phase regions; defining edges of the assigned phaseregions; establishing a boundary around the added edges; and assigningarea outside of the established boundary to have phase zero.
 4. Themethod of claim 3, wherein the phase areas are assigned a phase angle ofeither 0 or
 180. 5. The method of claim 4, further comprising generatinga trim mask to remove undesired patterns between phase 0 and phase 180regions.
 6. The method of claim 1, wherein the narrow line has a widthof a minimum gate width dimension.
 7. The method of claim 1, furthercomprising defining a boundary around edges of a second phase region,wherein the edges are not adjacent the critical poly region.
 8. Themethod of claim 7, wherein defining the boundary includes defining aboundary around edges having phase
 0. 9. The method of claim 1, furthercomprising defining break locations where phase transitions are mostlikely to occur.
 10. The method of claim 9, wherein the break locationshave a width that permits patterning and inspection.
 11. The method ofclaim 1, further comprising generating a trim mask to remove undesiredpatterns between first and second phase regions.
 12. A method ofgenerating phase shifting patterns to improve the patterning of gatesand other layers needing sub-nominal dimensions, the method comprising:defining critical gate areas including critical gate area edges;creating phase areas on either side of the critical gate areas, thephase areas having first edge, the first edges being different than thecritical gate area edges; assigning opposite phase polarities to thephase areas on either side of the critical gate areas; enhancing phaseareas with assigned phase polarities; defining break regions where phasetransitions are likely to occur; generating polygons to define otheredges and excluding the defined break regions; and constructing aboundary region along the first edges to form a phase region boundary.13. The method of claim 12, further comprising: correcting design ruleviolations; and applying optical proximity and process corrections tophase regions to allow proper pattern generation.
 14. The method ofclaim 12, further comprising generating a trim mask to remove undesiredpatterns between phase 0 and phase 180 regions outside of a desiredpattern.
 15. The method of claim 14, wherein the generating is done byoversizing boundary and break regions.
 16. The method of claim 14,wherein the chrome border has a width of a distance between phase 0 andphase 180 regions.
 17. A method of enhancing clear field phase shiftmasks with a chrome border around outside edges of phase 0 and phase 180regions, the method comprising: assigning phase polarities to phaseareas, the phase areas including first phase areas and second phaseareas; defining first edges of the assigned phase areas, the first edgesbeing edges of a critical poly region; establishing a first boundaryaround the defined added edges of the first phase area, the added edgesbeing different than the first edges; forming a chrome border in thefirst boundary around the first phase area; establishing a secondboundary around the added edges of the second phase area; and forming aphase shift border in the second boundary around the second phase area.18. The method of claim 17, wherein adding edges to the assigned phaseareas includes defining break regions where phase transitions occur andgenerating polygons including edges but excluding break regions, whereinthe polygons are merged with the assigned phase areas.
 19. The method ofclaim 17, further comprising generating a trim mask to remove undesiredpatterns between the first and second phase areas.
 20. The method ofclaim 19, wherein the trim mask does not cover all or any of the phaseshift border in the second boundary around the second phase area. 21.The method of claim 19, wherein the generating is done by oversizing theboundary and break regions.
 22. A mask configured for use in anintegrated circuit manufacturing process, the mask comprising: acritical poly section defined by first edges of a phase zero region andfirst edges of a phase 180 region; a first chrome boundary regionlocated outside second edges of the phase 180 region, the second edgesof the phase 180 region being different than the first edges of thephase 180 region, wherein the chrome boundary region includes an opaquematerial; and a second chrome boundary region around second edges of thephase 0 region, the second edges of the phase 0 region being differentthan the first edges of the phase 0 region.
 23. The mask of claim 22,further comprising a region outside of defined areas having a phase ofzero.
 24. The mask of claim 22, wherein the second boundary regionincludes an opaque material.